Knight's rig had been involved in a collision with the rig of Cliff Cunningham, but Fraser said it's not yet clear whether it was the collision that caused the injury.

"Both teams finished the race but immediately after our veterinarian discovered that one of Knight's horses had suffered a fractured leg, and after further assessment the veterinarian made the decision to euthanize the horse," Fraser said.

"We have to determine whether the collision caused the horse's leg to break ... or whether that leg might have broken elsewhere during the race."

The chuckwagon safety commission has asked to review the race and will interview the drivers and judges Saturday morning.

However, Fraser noted the judges immediately fined rookie driver Cunningham -- who is competing at the Stampede for the first time -- $2,500 for interference, which means he either cut off the other team or allowed his rig to bump the other team's rig.

Fraser said the safety commission could increase or decrease that fine depending on their findings.

One week ago, one of Cunningham's horses had to be destroyed after suffering a broken leg during a chuckwagon race on the Stampede's first night of competition.

Fraser said in that case, a review concluded the horse suffered a "catastrophic" injury that was not the result of driver error or a collision.

"It's unfortunate Mr. Cunningham is having a bit of a rough go at it as a rookie," said Fraser. "I'm sure nobody feels worse than Cliff Cunningham."

There are still two days to go in the competition, but overall Stampede officials have been having a better year than 2010, when six horses had to be destroyed.

Two died of heart attacks, two were destroyed after suffering injuries and another broke its back from bucking too hard.

The sixth died after experiencing health difficulties 40 minutes after a chuckwagon race.

Animal welfare organizations complained that rodeo is simply cruelty masquerading as entertainment. In Britain, a group called League Against Cruel Sports called on Ottawa to end ``the immense cruelty'' inherent in rodeos and suggested to British travel agencies that they refuse to offer vacation packages to the Stampede.

More than 50 MPs signed a motion in the British House of Commons that asked the Canadian government to improve how animals were treated at the rodeo.

Stampede officials instituted an overhaul of animal care standards at the event, including microchipping horses to track how often they are used and cutting the number outriders in the chuckwagon races to two from four.

"In general terms, we've had a relatively safe event," Fraser said Friday. "Unfortunately, we've had these two horses die and we have to continue to try and improve our system. It's not just a one-year fix."

He said the goal is always to have no animal deaths, but pointed to comments recently made by noted animal science expert Dr. Temple Grandin who argued rodeos themselves are not at fault.

"It's the way breeding has taken place over the last 30 or 40 years," Fraser said, summarizing Grandin's argument. "These horses are bred so that they're big and powerful but not necessarily as strong as they could be."

That hasn't placated animal welfare organizations such as the Vancouver Humane Society, which has noted more than 50 chuckwagon horses have died since 1986.

After the first horse death a week ago, the society called for the immediate suspension of the Stampede chuckwagon races.

"The Stampede's claims to have made the race safer have been proven false," society spokesman Peter Fricker said at the time.

"It is totally unacceptable to continue this event when horse after horse is dying just to entertain a crowd."